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From:   Rudolf Marek <r.marek@assembler.cz>
Subject: [PATCH] x86: make X86_BUG_FXSAVE_LEAK detectable in CPUID on AMD
References: <558a0f66-002b-7365-9988-9877b95a2c31@assembler.cz>
 <20171118180538.e7b5l4r2j5l5esjd@pd.tnic>
 <4813068b-f669-5239-f3a4-6e57af77be4c@assembler.cz>
 <20171119103001.ncjck5wbzaqyqewo@pd.tnic>
To:     Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>,
        "H. Peter Anvin" <hpa@zytor.com>, x86@kernel.org
Cc:     andy Lutomirski <luto@amacapital.net>,
        Borislav Petkov <bp@suse.de>,
        lkml <linux-kernel@vger.kernel.org>
Message-ID: <bdcebe90-62c5-1f05-083c-eba7f08b2540@assembler.cz>
Date:   Tue, 28 Nov 2017 22:01:06 +0100
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The latest AMD AMD64 Architecture Programmer's Manual
adds a CPUID feature XSaveErPtr (CPUID_Fn80000008_EBX[2]).

If this feature is set, the FXSAVE, XSAVE, FXSAVEOPT, XSAVEC, XSAVES
/ FXRSTOR, XRSTOR, XRSTORS always save/restore error pointers,
thus making the X86_BUG_FXSAVE_LEAK workaround obsolete on such CPUs.

Signed-Off-By: Rudolf Marek <r.marek@assembler.cz>
Reviewed-and-tested-by: Borislav Petkov <bp@suse.de>

---
 arch/x86/include/asm/cpufeatures.h | 1 +
 arch/x86/kernel/cpu/amd.c          | 7 +++++--
 2 files changed, 6 insertions(+), 2 deletions(-)

diff --git a/arch/x86/include/asm/cpufeatures.h b/arch/x86/include/asm/cpufeatures.h
index c0b0e9e..800104c 100644
--- a/arch/x86/include/asm/cpufeatures.h
+++ b/arch/x86/include/asm/cpufeatures.h
@@ -266,6 +266,7 @@
 /* AMD-defined CPU features, CPUID level 0x80000008 (EBX), word 13 */
 #define X86_FEATURE_CLZERO		(13*32+ 0) /* CLZERO instruction */
 #define X86_FEATURE_IRPERF		(13*32+ 1) /* Instructions Retired Count */
+#define X86_FEATURE_XSAVEERPTR		(13*32+ 2) /* Always save/restore FP error pointers */
 
 /* Thermal and Power Management Leaf, CPUID level 0x00000006 (EAX), word 14 */
 #define X86_FEATURE_DTHERM		(14*32+ 0) /* Digital Thermal Sensor */
diff --git a/arch/x86/kernel/cpu/amd.c b/arch/x86/kernel/cpu/amd.c
index d58184b..bcb75dc 100644
--- a/arch/x86/kernel/cpu/amd.c
+++ b/arch/x86/kernel/cpu/amd.c
@@ -804,8 +804,11 @@ static void init_amd(struct cpuinfo_x86 *c)
 	case 0x17: init_amd_zn(c); break;
 	}
 
-	/* Enable workaround for FXSAVE leak */
-	if (c->x86 >= 6)
+	/*
+	 * Enable workaround for FXSAVE leak on CPUs
+	 * without a XSaveErPtr feature
+	 */
+	if ((c->x86 >= 6) && (!cpu_has(c, X86_FEATURE_XSAVEERPTR)))
 		set_cpu_bug(c, X86_BUG_FXSAVE_LEAK);
 
 	cpu_detect_cache_sizes(c);
-- 
2.7.4


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